backport: Bump k256 to v0.10 (#1059)

[thanethomson]

Backport of #1059 for v0.23.x.

[codecov-commenter]

Codecov Report

Merging #1060 (bdd1293) into v0.23.x (8aabc22) will decrease coverage by 0.1%.
The diff coverage is 100.0%.

@@            Coverage Diff            @@
##           v0.23.x   #1060     +/-   ##
=========================================
- Coverage     66.3%   66.1%   -0.2%     
=========================================
  Files          209     209             
  Lines        20974   21023     +49     
=========================================
- Hits         13918   13917      -1     
- Misses        7056    7106     +50     

Impacted Files	Coverage Δ
tendermint/src/time.rs	99.6% <100.0%> (ø)
tendermint/src/private_key.rs	23.8% <0.0%> (-35.1%)	⬇️
testgen/src/header.rs	79.3% <0.0%> (-1.6%)	⬇️
testgen/src/commit.rs	90.6% <0.0%> (-0.7%)	⬇️
tendermint/src/node.rs	63.5% <0.0%> (-0.2%)	⬇️
light-client/src/types.rs	38.9% <0.0%> (+0.2%)	⬆️
tendermint/src/public_key.rs	75.0% <0.0%> (+0.5%)	⬆️
testgen/src/vote.rs	85.7% <0.0%> (+0.8%)	⬆️

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